1. Field of the Invention
The present invention relates to a technology of exchanging electronic values as information electronically representing values.
2. Related Background Art
There is the conventionally proposed technology of safely circulating information electronically representing values (hereinafter referred to as “electronic values”), including electronic money and electronic tickets. For example, the original data circulation method disclosed in Japanese Patent Application Laid-Open No. 2001-143009 implements safe circulation by enabling device-device exchange and use of electronic values issued to users, while preventing reproduction and forgery of the electronic values.
The above original data circulation method provides the safety of circulation but does not always assure fairness of trade. Here the fair trade is a trade satisfying the condition that “neither of two parties involved in an attempt of mutual exchange of electronic values loses the electronic value of itself, without acquiring an electronic value as a consideration or without obtaining a guarantee for acquisition thereof”. Namely, in the case of the aforementioned original data circulation method, when an exchange transaction is interrupted, for example, by an abnormality of communication or a fraud of a transaction partner on the occasion of exchanging electronic values E1, E2 held by respective devices D1, D2 of users, D1 could lose E1 without acquisition of E2.
A document disclosing a technology to overcome this disadvantage is, for example, Japanese Patent Application Laid-Open No. 2004-341643. This technology enables an exchange of electronic values in a transaction under a normal condition, i.e., in a transaction satisfying the condition that a communication line between the devices D1 and D2 is not interrupted from start to end of the transaction and that D1 and D2 both cooperate to fulfill the transaction. On the other hand, under abnormal conditions, a third-party device is used to enable recovery of fairness of the transaction even from a midway point of the transaction.